Response of the rhizospheric soil microbial community of sugar beet to nitrogen application: A case of black soil in Northeast China

Nitrogen (N) is the most crucial mineral element for the growth of sugar beet (Beta vulgaris L.) plant. Rational application of N fertilizer is known to increase sugar beet yields and influence the rhizospheric microbial communities, but there is an uncertainty about the response of sugar beet rhizosphere soil microbes to the seasonal nitrogen fertilizer application in black soil region of northeast China. Under field conditions, we set up nitrogen (N 90 kg / ha) and no nitrogen (N 0 kg / ha) treatments. Soil chemistry and high-throughput sequencing analysis were carried out on the soil samples of sugar beet rhizosphere at harvest. Application of N fertilizer significantly increased rhizospheric soil bacterial diversity and reduced bacterial and fungal abundance and fungal diversity. Post-N fertilization, the dominant bacterial groups were Actinobacteria, Proteobacteria, Firmicutes, and the dominant fungal groups were Ascomycota and Mortierellomycota. The community structure of sugar beet rhizospheric bacteria and fungi was significantly altered. Redundancy analysis showed that organic matter (OM), available nitrogen (AN) and available potassium (AK) were the main soil properties affecting soil bacterial community structure, whereas fungal community structure was affected by AK, pH and available phosphorus (AP). FAPROTAX analysis demonstrated that fermentation is the main metabolic mode of sugar beet rhizosphere soil microorganisms, followed by nitrification, automatic compound degradation, manganese oxidation and hydrocarbon degradation. Analysis of the KEGG metabolic pathways revealed that N fertilization enhances the abundance of xenobiotics biodegradation and metabolism; moreover, the transport and catabolism pathways increased after nitrogen fertilization. The application of N fertilizer affected the diversity of microbes, changing the composition and structure of bacterial and fungal communities, which consequently changed the ecological environment of sugar beet rhizosphere in northeastern black soils.